The invention relates to an exhaust gas control system and to an exhaust gas control method. The exhaust gas control system has an exhaust gas throttle valve in an exhaust gas duct and an actuation device for the exhaust gas throttle valve. The actuation device has an actuating linkage. An exhaust gas pressure control device controls the exhaust gas pressure occurring in the exhaust gas duct upstream of the exhaust gas throttle valve. An exhaust gas control system of this kind with an exhaust gas throttle valve has many applications in internal combustion engines, preferably in internal combustion engines of motor vehicles.
The fact that an exhaust gas control system of this kind can be used as an exhaust brake is known from printed publication DE 198 21 130 A1. In this case, the flow of exhaust gases from the internal combustion engine is prevented by an exhaust brake flap in order to achieve an increase in the power of the engine brake. For this purpose, the exhaust tract is sealed as tightly as possible, and the injection pump is simultaneously switched to zero delivery. In this state, the engine is driven by the overrunning motor vehicle, and the pressure rises owing to the compressor action of the engine.
Unless an exhaust gas control system is provided, a rise in the pressure upstream of the exhaust brake flap can have the effect that cylinder valves of the engine are disadvantageously forced open and exhaust gas flows back into other cylinders. Another risk associated with a solution of this kind involving an exhaust brake flap to assist engine braking performance is that, after additional cylinder valves have been forced open, an increased amount of gas is pumped backward and forward between the exhaust gas duct and the individual cylinders, with the result that a large amount of heat is generated, causing the temperature upstream of the exhaust brake flap to rise.
In order to limit the rise in pressure and temperature, DE 198 21 130 discloses an exhaust gas control system 50 of the type shown in FIG. 7, with an exhaust brake flap or throttle flap 12. In order to achieve pressure and temperature limitation, the throttle flap 12 has a pressure limiting valve 35 arranged on the throttle flap 12. When closed, the pressure limiting valve 35 keeps an opening 37 in the throttle flap 12 closed under a preload by means of a valve flap 36. The preload is applied by a leaf spring 38, as FIG. 7 shows. The valve flap 36 of the pressure limiting valve 35 opens as soon as a permissible exhaust gas pressure P1 upstream of the throttle flap 12 is exceeded and hence also as soon as an impermissibly high temperature T1 in the exhaust gas duct 5 would arise. By means of the pressure limiting valve 35, the engine is thus protected from excess pressure and excess temperature in a braking phase.
A dynamic pressure-limiting exhaust gas control system 40, which is shown in FIG. 8, is known from U.S. Pat. No. 4,750,459. For this purpose, the exhaust gas control system 40 has a butterfly throttle flap 13. When closed, an edge surface of the butterfly throttle flap 13 is sealed off in a zone 41 by a valve head 42 of a pressure relief valve 43. When a permissible upstream exhaust gas pressure P1 is exceeded, the pressure relief valve 43 opens a bypass, via which an excess pressure and hence also an excessive increase in temperature can be reduced.
An exhaust gas control system 60 of the type shown in FIG. 9, which operates with an asymmetrically arranged throttle flap 12, is furthermore known from U.S. Pat. No. 5,355,673. Here, the throttle flap 12 can be pivoted about a pivot 28 arranged outside the axis of symmetry of the exhaust gas duct 5. In a closed state of the asymmetrically mounted throttle flap 12, which can be held in the closed state by means of a spring element, the spring elastic preload is overcome when there is an excess pressure upstream of the throttle flap, and the preloaded throttle flap 12 opens a gap, via which the excess pressure and hence an excess temperature upstream of the throttle flap 12 can be reduced.
By virtue of the known exhaust gas control systems, it is thus impossible to exceed a maximum permissible pressure at a maximum engine speed. With these solutions, the backpressure of the engine exerts an opening force which overcomes the closing spring mechanism in the known solutions. However, this has the disadvantage that either the throttle flap itself or at least the limiting valve vibrates or flutters continuously owing to the pulsating pressure in the exhaust gas duct since the engine does not discharge the gas in a constant stream but rather in phases in accordance with the piston strokes. This means that exhaust gas control systems of this kind are subject to severe wear and a short service life, and it can additionally lead to severe noise generation.
It is the object of the invention to overcome the disadvantages of the prior art and to specify an exhaust gas control system which not only uses the rise in pressure upstream of a closed exhaust gas throttle flap for an exhaust flap brake but also uses to advantage the rise in temperature, associated with the rise in pressure, in the exhaust gas duct upstream of an exhaust gas throttle valve.
This object is achieved according to the invention by an exhaust gas control system and an exhaust gas control method, wherein the exhaust gas control system has an exhaust gas throttle valve in an exhaust gas duct and an actuation device for the exhaust gas throttle valve. The actuation device has an actuating linkage. An exhaust gas pressure control device controls the exhaust gas pressure occurring in the exhaust gas duct upstream of the exhaust gas throttle valve. For this purpose, the actuating linkage has a control actuator which interacts with a pressure compensation volume. In this arrangement, the pressure compensation volume is connected pneumatically to a restrictor opening upstream of the exhaust gas throttle valve.
One advantage of this exhaust gas control system is that the pressure upstream of the exhaust gas throttle valve is introduced into a compensation volume via the restrictor opening and is passed from said volume to an actuator which, as a function of the pressure directly applied to the actuator, can transfer the exhaust gas throttle valve stably from a closed position to a position controlled as a function of pressure by way of the linkage. The restrictor opening in conjunction with the compensation volume gives rise to a delay element which to a large extent filters high-frequency pressure peaks out of the pulsating exhaust gas pressure in an advantageous manner. By adaptation of the exhaust gas throttle valve and of the output volume, it is possible to set the filter behavior of this delay element so that both high-frequency fluttering of the exhaust gas throttle valve and excess pressure over a prolonged period can be avoided with the exhaust gas control system according to the invention. The compensation volume gives rise to a somewhat slow mean pressure rise, but this does not lead to additional cylinder valves being forced open since the control actuator in the actuating linkage enables the exhaust gas pressure, and an exhaust gas temperature determined by the exhaust gas pressure, to be controlled upstream of the exhaust gas throttle valve.
At the same time, the exhaust gas pressure control device preferably has an exhaust gas pressure limiting device, which makes it possible to limit the exhaust gas pressure upstream of the exhaust gas throttle valve.
For pressure control or pressure limitation, the exhaust gas throttle valve can have a throttle flap, which interacts via a pivot with the actuating linkage and hence also with the control actuator. Instead of a throttle flap, the exhaust gas throttle valve preferably has a butterfly throttle flap which is of completely symmetrical configuration with respect to a pivoting axis, the pivoting axis coinciding with an axis of symmetry of the exhaust gas duct in the region of the throttle valve. A butterfly throttle flap of this kind has the advantage that the required adjustment forces at the throttle flap axis are minimal.
In a preferred embodiment of the invention, the actuation device has a drive which assumes two end positions, with a first end position, in which the actuating linkage and the control actuator hold the exhaust gas throttle valve in an open position. In a second end position of the drive, the control actuator comes into effect, and the exhaust gas throttle valve is held in a position determined by the exhaust gas pressure of the pressure compensation volume. Owing to the evened out pressure in the compensation volume, this position is completely stable and hence fluttering of a throttle flap, in particular a butterfly throttle flap, does not occur.
In order to achieve the two end positions of the drive, the drive can have an electromagnetically operated piston. Solenoid drives of this kind have the advantage that they can move relatively rapidly between the two end positions of the linkage.
In another embodiment of the invention, the drive has a hydraulically operated piston, a drive of this kind allows the two end positions to be assumed in a damped manner.
In another embodiment of the invention, the drive has a pneumatically operated piston, it being possible for a pneumatic drive of this kind to be varied in an advantageous manner in its motion sequence for the linkage.
In this arrangement, the control actuator is connected mechanically to the piston of the drive. This mechanical connection includes both direct fixing of the control actuator on the piston and transfer of the motion of the drive to the control actuator via a corresponding connecting rod. Here, a relatively large control range for the exhaust gas pressure-determined position of the exhaust gas throttle valve can be associated with direct fixing of the actuator on the piston, while the pressure-dependent deflection of the linkage can be reduced correspondingly with the aid of a connecting rod.
For a hydraulic or pneumatic drive, provision is made for the actuation device to have an operating cylinder, a piston and a connecting rod, which is preloaded in a spring-elastic manner in a first, inactive state of the operating cylinder. Here, the operating cylinder is fixed in an articulated manner at an end situated opposite the connecting rod. This articulated fixing can advantageously compensate for a circular motion of a lever arm about the pivot of the exhaust gas throttle valve as the exhaust gas throttle valve is moved from an open position into a closed position and vice versa if both the stroke motion of the connecting rod and the stroke motion of the control actuator take place in a straight line and are connected to the lever arm via a joint.
The control actuator can be of similar construction to the drive with a drive piston. For this purpose, the control actuator preferably has an actuator cylinder with an actuator piston preloaded in a spring-elastic manner and an actuator rod fixed on the actuator piston. The free end of the actuator rod is pivotally attached to a lever arm which interacts with a pivot of the exhaust gas throttle valve. In this arrangement, the control actuator comes into effect only when the exhaust gas throttle valve is in a closed position and an excess pressure and an excess temperature dependent on the pressure builds up in the exhaust gas duct upstream of the exhaust gas throttle valve. Only then is the pressure compensation volume charged via the restrictor opening upstream of the exhaust gas throttle valve and can set in motion the actuator or actuator piston if an impermissibly high maximum pressure, at which there is a risk that additional cylinder valves will be forced open, builds up.
In order to allow interaction between the pressure compensation volume and the actuator cylinder, the actuator cylinder has an opening which is connected pneumatically to the pressure compensation volume. In a reduced-pressure state of the pressure compensation volume, the lever arm, which is pivotally attached to the actuator rod, has a maximum deflection and, in a pressurized state of the pressure compensation volume, the lever arm has a deflection controlled as a function of pressure.
Here, the length of the actuating linkage, which is made up of the connecting rod of the drive and the actuator rod of the control actuator, is in practice shortened. As already mentioned above, if there is a requirement for a larger deflection of the linkage, the actuator cylinder can be mounted directly on the drive piston, something that may preferably be advantageous for cleaning a diesel particle filter (DPF) in order to allow greater temperature variation upstream of the exhaust gas control valve with the engine running and fuel injection switched on.
In a preferred embodiment of the invention, a pressure compensation volume container is arranged at the restrictor opening of the exhaust gas duct upstream of the exhaust gas throttle valve. The pressure compensation volume container is connected to the opening of the actuator cylinder via a pressure line. In this arrangement, the pressure line is of a flexible design to enable it to follow the movements of the actuating linkage and hence the movements of the actuator cylinder.
In another preferred embodiment of the invention, the pressure compensation volume and the control actuator are arranged in a common container. This has the advantage that the number of components of the exhaust gas control system can be reduced, and this is advantageous for storage costs, spare parts costs and assembly costs.
Provision is furthermore made to design the connecting rod as a hollow cylinder, with the hollow cylinder having the control actuator. A hollow cylinder of this kind is thus seated directly on the drive piston of the drive, and the length of the hollow cylinder therefore determines the possible maximum actuator stroke at the lever arm for actuating the exhaust gas throttle system. Moreover, the hollow cylinder designed as a connecting rod can form a common housing for both the control actuator and the pressure compensation volume. In this case, the number of components that have to be provided for the exhaust gas control system is further reduced since not only is the connecting rod eliminated but the hollow cylinder can also simultaneously form the piston for the drive in the drive cylinder.
Moreover, provision is made for the exhaust gas throttle valve to be arranged downstream of an exhaust manifold of an internal combustion engine and upstream of a DPF. In this case, the exhaust gas throttle valve in conjunction with the exhaust gas control system serves as an exhaust throttle flap brake, which can be activated when fuel injection into the engine is switched off. On the other hand, the exhaust gas throttle valve can be arranged downstream of a DPF of an internal combustion engine and upstream of an exhaust muffler. In this case, the increase in the exhaust gas temperature associated with the rise in pressure in the exhaust gas duct can be used, for example, to clean the DPF by heating it up, while the injection process or injection of fuel into the engine is not switched off.
Such cleaning can take place both periodically while the vehicle is being driven and while the vehicle is stationary with the engine running. Since the engine does not operate as a compressor in this case but, on the contrary, supplies hot exhaust gases, a larger pressure-dependent deflection of the control actuator is helpful, as allowed by one of the embodiments of the invention described below, in order to be able to carry out an optimum temperature cycle for the cleaning of the DPF, e.g. while the vehicle is being driven.
An exhaust gas control method involving an exhaust gas control system has the following method steps. First of all, an exhaust gas throttle valve is provided in an exhaust gas duct, being adjustable by way of an actuating linkage of an actuation device. An exhaust gas pressure control device for the pulsating exhaust gas pressure occurring in the exhaust gas duct upstream of the exhaust gas throttle valve is furthermore provided. Additionally provided upstream of the exhaust gas throttle valve is a restrictor opening, which feeds the pulsating exhaust gas pressure to a pressure compensation volume which compensates for pressure peaks in the pulsating exhaust gas pressure and feeds the compensated exhaust gas pressure to a control actuator.
In a first end position of a drive, an actuating linkage with the control actuator holds the exhaust gas throttle valve stably in an open position. In a second end position of the drive, the actuating linkage with the control actuator holds the exhaust gas throttle valve in a stable position controlled by the applied pressure in the pressure compensation volume. An exhaust gas control method of this kind can be used in an advantageous manner both for an exhaust flap brake and for cleaning and regeneration processes in a DPF.
In this exhaust gas control method, in a closed position of the exhaust gas throttle flap, the pressure upstream of an exhaust gas throttle flap is fed to the pressure compensation volume via a restrictor opening, and the compensated exhaust gas pressure is supplied to an actuator, which opens the exhaust gas throttle flap in a manner controlled as a function of the compensated exhaust gas pressure. Here, the restrictor opening and the pressure compensation volume form a delay element with a filter effect, in which pressure peaks in the pulsating exhaust gas pressure are reduced or filtered out, with the filtering behavior being set so that the exhaust gas throttle flap can assume a stable position controlled as a function of pressure.
In this exhaust gas control method, a first open position is maintained by the exhaust gas throttle valve for as long as a drive of an actuation device is inactive and maintains a first end position. As soon as the drive of the actuation device is activated and assumes a second end position, in which the control actuator is in a setting controlled by the pressure of the pressure compensation volume, the exhaust gas throttle valve is accordingly transferred from a closed position to a pressure-dependent second controlled stable position.
Here, the drive can drive a piston in an operating cylinder electromagnetically, hydraulically or pneumatically and move it from a first end position to a second end position.
In a preferred implementation of the method, a lever arm, which interacts with a pivot of the exhaust gas throttle valve and is pivotally attached to a free end of an actuator rod, is moved as a function of pressure by an actuator piston of an actuator cylinder. For this purpose, the actuator cylinder is connected pneumatically to the pressure compensation volume via an opening. In a reduced-pressure state of the pressure compensation volume, the lever arm, which is pivotally attached to the actuator rod, assumes a maximum deflection and, in a pressurized state of the pressure compensation volume, the control actuator imparts to the lever arm a deflection controlled as a function of pressure.
The exhaust gas control method can be employed to boost engine braking if the exhaust gas throttle valve is arranged downstream of an exhaust manifold of an internal combustion engine and upstream of a soot particle filter of an engine system, and the pressure in the exhaust manifold is controlled in such a way by use of the exhaust gas throttle valve that a maximum permissible pressure in the internal combustion engine and a pressure-dependent maximum permissible temperature are not exceeded during a corresponding braking process with the fuel injection switched off.
It is furthermore possible to use the exhaust gas control method to heat the exhaust gas duct in order thereby to clean a DPF. For this purpose, the exhaust gas throttle valve is arranged downstream of a soot particle filter of an internal combustion engine and upstream of an exhaust muffler, and the pressure in the exhaust gas duct is controlled in such a way by use of the exhaust gas throttle valve that a maximum permissible pressure in the internal combustion engine is not exceeded and that, with fuel injection switched on, a pressure-dependent maximum permissible temperature in the DPF is not exceeded during cleaning of the DPF.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.